1. Field of the Invention
This invention relates to communications and more particularly to electrical echo systems for underwater use.
2. Description of the Prior Art
Echo systems such as fish finders and the like are well known to the art. These systems generally transmit a short pulse of acoustical energy into the body of water by a transmitter transducer. The transmitted acoustical wave front generally propagates in a spherical manner within a conical volume with the vertex of the cone being at the transmitter transducer and the base of the cone being the bottom of the body of water. The transmitted wave front expands within the conical volume as a function of distance and may cover a very large area on the bottom of the body of water and other objects are received by a receiver transducer which may be one and the same as the transmitter transducer or be a separate unit. The transmitted wave front reflecting from the bottom of the body of the water and other objects results in a series of reflected wave fronts. This series of reflected bottom wave fronts appears as an output commonly referred to as "bottom smear." The cone of investigation can include reflected pulses from fish and obstructions which are in front of the vessel in which the echo system is installed. Thus, the system may be used to warn of an impending obstruction to provide time for the vessel to avoid the obstruction. Since the transmitted acoustical wave front widens with distance from the transmitter transducer, an obstruction in front of the vessel will appear as an object immediately under the vessel, but, at a greater distance than the bottom. Accordingly, the obstruction will be lost within the bottom smear until it emerges as a rise in the bottom profile. Consequently, the early warning or the detection of objects in front of the vessel is totally eliminated.
Attempts to overcome such difficulties have centered around methods of utilizing the difference in amplitude between the relatively weak reflected wave fronts from fish and the stronger reflected wave fronts from the bottom, U.S. Pat. No. 3,440,598 discloses an apparatus wherein a grey line is interposed between the initial bottom reflected signal and the remainder of the bottom smear, whereas U.S. Pat. No. 3,098,210 discloses an apparatus wherein a white line is interposed between the initial bottom reflected signal and the remainder of the bottom smear. Other methods and apparatuses have included separate channels for the fish and bottom signals and the like. However, little attention has been directed to the fundamental problem of eliminating the obliterating bottom smears to resolve a signal which is located within the bottom smear.
Therefore, an object of this invention is to overcome the aforementioned disadvantages of the prior art grey line and white line apparatuses and provide a device for detecting an object in a body of water which eliminates the bottom smear caused by a series of reflected wave fronts from the bottom of the body of water.
Another object of this invention is to provide a device for detecting the presence of an object in a body of water which provides an output which is substantially independent of the continuance in time of the receiver output caused by a series of wave fronts reflecting from the bottom of the body of water.
Another object of this invention is to provide a device for detecting the presence of an object in a body of water whereby the wide bottom smear of the receiver output caused by the series of wave fronts reflecting from the bottom will appear as narrow bottom lines depending on the bottom strata, etc.
Another object of this invention is to provide a device for detecting the presence of an object in a body of water having an accentuator circuit for resolving a receiver output corresponding to the reception of a wave front reflecting from an object in the body of water which occurs within the time interval of the bottom smear encountered by the prior art units.
Another object of this invention is to provide a device for detecting the presence of an object in a body of water including means for establishing a threshold level for signals transfer whereby signals below the threshold level will be blocked whereas signals above the threshold level will be transferred to a display.
Another object of this invention is to provide a device for detecting the presence of an object in a body of water which is readily adaptable to existing echo systems and the like.